Medical devices, such as, for example nuclear or scintillation or gamma cameras are conventionally used to perform Single Photon Emission Computed Tomography (SPECT) studies. A patient may ingest a radiopharmaceutical, such as Thallium or Technetium, which emits gamma radiation from a body organ which is the subject of a medical study. The gamma camera detects the radiation and generates data indicative of the position and energy of the radiation which is then mathematically corrected, refined and processed through a procedure known as reconstruction tomography (performed by a computer) to produce pictures of scintigrams (two or three dimensional) of the body organ which is the subject of the study.
Different radiopharmaceuticals produce gamma rays having different energies typically expressed as photopeak energy in electron volts corresponding to the output pulse generated by a photomultiplier tube (“PMT”) in response to a scintillation produced by a crystal when struck by a gamma ray. A gamma camera may be fitted with two detector heads, each of which is fitted with a collimator and each head extends in a two dimensional plane, referred to herein as the x, y plane. Each head contains an array of photomultipliers which are arranged behind a scintillation crystal. The PMT's generate analog pulse signals in response to the scintillations produced by the crystal when struck with gamma rays passing through the collimator which indicate the energy of the gamma ray, i.e., the photopeak signal. The pulse signals are grouped, digitized, corrected and processed as data indicative of position, x, y, and energy, z. This data correlates to a pixel of a 2 dimensional picture spanning or encompassing the area of the detector head. A two head gamma camera will simultaneously generate two such pictures or scintigrams (a 3 head camera will generate 3 pictures, etc), each of which may be viewed as being similar to an x-ray. The heads will then typically rotate about the body and generate additional pictures which are then assembled together to make a 3 dimensional view of the object precisely pinpointing the shape of any abnormality emitting gamma radiation within the organ.
Gamma cameras are fitted with removable grids, such as for example, collimators having varying thicknesses for collimating gamma rays of various energies. Collimators in gamma cameras absorb angular rays in the septa so that only parallel rays pass through and strike the crystal. For higher energy gamma rays, the thickness or depth of the passages or channels in the collimator has to increase to absorb the cross channel and slightly angular rays which would otherwise pass through the collimator. Gamma cameras are thus typically supplied with thin, medium and thick removable and interchangeable collimators sized to cover the energy spectrum of the gamma radiation used in SPECT studies. These collimators must be repositioned each time they are changed.
Collimators that restrict the direction of gamma rays impinging on scintillation detectors may be used for imaging distributions of single photon emitting radionuclide. These devices are heavy, due to their construction from dense, high-Z materials, and may be retained on moving detector heads, which may be used to generate data for single photon emission computed tomography (SPECT), i.e. three-dimensional tomographic imaging. Different collimators are often used for different imaging tasks, such as for example using different radionuclide that emit different energy gamma rays, or selecting a desired combination of resolution and sensitivity. When exchanged, collimators must be positioned and repositioned in a precise, repeatable fashion in order to maintain, for example, calibration, either for accurate correction and calculation of gamma-ray projections or correction for flood non-uniformity, due to collimator fabrication inaccuracies.
Small animal SPECT imagers may employ collimators with one or more pinholes to enable high resolution imaging by magnification of the object space onto the detector. Heavy tungsten alloy plates or lead alloy plates with tungsten or gold inserts may be mounted to pyramidal lead alloy shields that hold the pinholes at the required focal length distance from the detector face.
In view of the prior art discussed above, there is a need to provide a grid and method allowing for simple, quick, and secure positioning and holding of the grid on the detector. This may maintain calibration. Hereby accurate correction and calculation of gamma-ray projections or correction for flood non-uniformity, due to grid fabrication inaccuracies, may be made.
Tools or fasteners may be judged to be a hazard because screw threads can be damaged by a user, and small items such as screws or tools might be dropped into a scanner. Consequently, easy installation and removal without the use of tools or fasteners is desired.
There is further a need to improve the quality of the images taken. The accurate positioning of an antiscatter grid, such as a collimator, does affect image quality.
There further exists a desire to reduce the time for setting up the medical device carrying the grid. A simple, quick, and secure positioning and holding of the grid on the detector may reduce the time for setting up the medical device.
There also exists a need to minimize the structure of the grid, the detector, and the medical device carrying the grid. It is desirable to have a light detector. Small and light detectors can be easily moved around the subject and in the medical device.
It is desirable to avoid cumbersome arrangements for positioning and holding a grid on a detector, in an economic and technical perspective.
Additionally, it is desirable to provide the necessary retention force while a detector is rotated 360 degrees, as well as precise repositioning when installing, and easy installation and removal without the use of tools or fasteners.